The present invention generally relates to a non-contact measurement apparatus and, in particular, relates to one such non-contact measurement apparatus having a bifurcated bundle of optical fibers, a first portion of which are adapted to receive light from a light source and a second portion of which are adapted to convey light to a light detector.
In general, one of the more common methods of optically determining the thickness of a lens, or other reflective surface, is by laser interferometry. In such an instrument, the laser is directed toward the surface and the reflected interferogram is formed in accordance with the rules of light cancellation or reenforcement depending upon the phase of the signals. For example, if the reflected light is one hundred and eighty degrees out of phase with the incident light the light reflected is canceled and a dark ring is exhibited on the interferogram. It is well known that laser interferometers are capable of measuring very small changes in the thickness of an optical material. However, such techniques are quite expensive and introduce problems relating to eye safety. Further, such techniques, to operate most efficiently, require a highly reflective surface.
Other methods and instruments for measuring the thickness of lenses include ultrasonic systems and astigmatic and knife edge focus systems. Typically, however, ultrasonic systems od not have high accuracy although they are relatively inexpensive. Astigmatic and knife edge focus systems are typically used in data storage systems and are affected by both surface tilt and surface quality.
Hence, it is highly desirable to provide a non-contact measuring apparatus for measuring the thickness of an object that is highly accurate and relatively inexpensive.